The rear cover of an electronics device is made up of two sections including an external heat sink and a rear cover frame. The iron oxide comprises ferrous oxide, ferrum dioxide, ferric oxide, ferroferric oxide, or combinations thereof. Electrode contacts are provided to at least two waveguide elements fabricated in the top silicon layer, each waveguide element having a thickness comparable to the top silicon layer thickness, a width of some hundreds of nm, and having a slot having dimensions in the range of 50-200 nm defined therebetween.